RE: Solenoid Radiator valves

["Kevin Hawkins" <lists@xxxxxxx>]

I have played quite a bit with the algorithms for the ON OFF control
=E2=80=
=93 which I have in about 4 rooms here. My problem comes because of the
hea=
t retention in the radiators. They are the very old fashioned cast iron
one=
s. Now as soon as the valve is opened they heat up very quickly (as the
wat=
er flowing past is already very hot) but they hold heat for a long time,
ca=
using the overshoot =E2=80=93 so I am faced with almost pulsing the valves
=
open for a very short time to only heat the radiator up a little. I even
pl=
ayed with a temp sensor attached to the radiator. Unfortunately this then
a=
lso gets complicated by the flow temp at the valve and the flow rate or
pre=
ssure =E2=80=93 both these being effected by other demands from TVR=E2=80=
=99s and zones. In one of the rooms the radiators are more modern meaning
t=
hey are far more efficient at radiating heat and hence cool much faster
=E2=
=80=93 this room I have managed to cater for the hysteresis far better
with=
an algorithm.=20

TBH I had intended all my valves to be proportional type 1 or raise/lower
t=
ype 2 below, but I had installed the traditional zone valves assuming I
cou=
ld just exchange the actuators at a later time for proportional ones
=E2=80=
=93 but you can=E2=80=99t get proportional or raise/lower exchange
actuator=
s for standard zone valves =E2=80=93 so I had to work around or fit new
val=
ves as well.

Neil =E2=80=93 when I said proportional I meant to include raise/=
lower in that category =E2=80=93 I think we are talking about three types
h=
ere aren=E2=80=99t we ??

1)       The type that is either fully open or fully closed (but takes a
fe=
w secs to move from one to the other)

2)       The type that you apply say 0-10V to and they are proportional ie
=
3V is 30% open

3)       The raise lower type =E2=80=93 you drive them with a succession
of=
pulses to move them from one position to the next ( or maybe even a timed =
voltage application) =E2=80=93 then they stay wherever they are left
=E2=80=
=93 if you drive them 2/3 open then that is where they stay. These take a
l=
ittle tracking and have to be calibrated against end positions
periodically=
=E2=80=93 I think these are the lowest cost of the 2 and 3 and what I will=
probably end up using.

There is a fourth type which is what most of my radiators use at the
moment=
=E2=80=93 it is a sort of =E2=80=98bodged=E2=80=99 TVR. Basically I have T=
VR=E2=80=99s with a capillary and remote sensor mounted in a small plastic
=
box. You set the required temperature on the standard mechanical rotary
TRV=
. However also mounted in the little sensor box is a small electric
element=
that applies heat to the sensor in proportion to the voltage applied to it=
. Hence you can set back that room by 2 degrees by applying 2V or by 5
degr=
ees by 5V etc. This works very well to regulate the room as the control is
=
effectively truly proportional =E2=80=93 you can also effectively turn a 
r=
oom ON or OFF this way. I am not sure these are manufactured anymore
=E2=80=
=93 they were made by Danfoss.

=20

I am really interested in this subject as I have yet to implement most of
m=
y control here =E2=80=93 so please do keep us updated on anything you find=
=E2=80=A6

=20

Kevin

=20

=20

-----Original Message-----
From: Dave McLaughlin [mailto:dave@xxxxxxx]=20
Sent: 07 April 2003 12:36
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves

=20

Hi Kevin,

I am also looking to replace mine with solenoid or proportional valves. Did
you have any kind of hysterisis in your control loop? Wouldn't adjusting
this have taken out the oscillations?

Regards
Dave...
-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]
Sent: 07 April 2003 01:17
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


You should also consider using a proportional valve rather than just
ON/OFF.
I have some ON/OFF ones and I still get oscillation around the setpoint
due
to retained heat (forgotten the tech word) within the radiators. (I was
basically using zone valves)

I have researched a few inline / TVR replacement options =E2=80=93 You ca=
n get
plain ON/OFF down to about =C2=A325 but proportional all seem to be circa=
=C2=A360
plus. There is a very low cost device (TVR replacement) that works on
thermal expansion =E2=80=93 basically you apply voltage and it heats and =
expands
but
the response time is quite slow.

Kevin


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